1. Field Of the Invention.
This invention relates in general to methods for treating incinerated waste products and the like, and more particularly, to treating incinerated municipal waste material to obtain free-from-ash ferrous metal, non-ferrous metals and/or metal-free ash as separate products.
2. Prior Art.
The increase in the volume and variety of solid waste products requiring disposal by both private and public sectors has grown dramatically. Such solid waste products have in the past been burned in mass burn or RDF incinerators. However, due to current environmental laws and regulations, incineration of solid waste has been restricted to a significant extent in many geographical areas, and in fact is prohibited in many areas today.
Disposal and burial of solid waste products in sanitary landfills is a frequently used alternative disposal method. But even this method is becoming non-acceptable in many geographical areas either because many existing landfills are reaching their capacity and additional replacement clean landfills have not been approved by regulatory agencies and authorities due to existing environmental laws and regulations and due to an actual shortage of land in some geographic areas.
Recovery of salvageable and recyclable metals, as well as "metal-free" ash, will reduce the amount of waste products that must be disposed. In addition any monies received for the recovered metals, particularly free-from-ash ferrous metals, or the metal-free ash may reduce the overall cost of treating the solid waste products. Most salvage methods involve pre-incineration separation of materials in the solid waste product, or after-incineration separation of the unburnt carboneous material from the recyclable metals and other material, or combination of these methods. Examples of the first method are disclosed in U.S. Pat. Nos. 3,524,594; 3,790,091 and 3,817,458, and examples of the other methods are disclosed in U.S. Pat. Nos. 4,113,185; 4,662,570; 4,815,667 and 5,067,659.
The treatment of incinerated waste products, particularly municipal waste products, presents numerous treatment problems. One significant problem is the diversity of the feedstock. It may include unburnt tree stumps, washing machines, metal bars, thin strands of wire, rocks, etc., all in various shapes and sizes, as well as significant quantities of ash. This diversity requires that the equipment be designed to handle this variety of materials.
Another significant problem is the abrasive characteristic of much of the incinerated waste material. This abrasiveness can wear out certain pieces of equipment in just hours or days. The resulting shut down time and equipment replacement cost can make a particular method uneconomical.
Still another problem is the moisture content of the incinerated waste material which makes the material tacky, particularly the wet ash. This tackiness can cause clogging or blinding problems with the equipment.
A further problem is plugging or jamming of equipment which can occur because of wire and similar material in the incinerated waste material.
All of these problems are particularly acute in the various screening devices typically used in such processes.
There are also in many cases the requirement that the process be designed so that the equipment can be positioned in restricted spaces, yet capable of handling enormous throughput of incinerated waste material.
Still another problem with existing processes when recovering free-from-ash ferrous metal from incinerated waste feedstock is the lack of consistent quality of the recovered ferrous metal. In most cases the ash content of the recovered ferrous metal is too high for the ferrous metal to be used in steel production and similar processes. Thus it must be sold at a much lower price as a low grade ferrous metal.
Another significant problem results from the combination of the large quantity of incinerated waste material that must be treated and the high percentage of ash material contained in the incinerated waste material. Prior treating processes do not efficiently separate the material being treated to reduce the time and wear on the processing equipment.
A still further problem has been the inability to process large quantities of feedstock in a manner that results in most of the ash being sufficiently metal-free to allow the ash to be used in building materials such as concrete. As a result, there is a greater processing cost per ton because a significant quantity of ash material must be disposed, rather than recycled in another product.